Aloha, Rankin:
This is a brilliant solution to my predicament with measuring the target height! Thank you!!!:beer:
But I may need to ditch the 360º prism idea for my control traverse. Looks like there is a question mark with its usage when it comes to accuracy.
Would you run your control traverse in a robotic mode? Kent had a concern about this earlier.
Granted I am not doing a first order survey here, but I want mold my mind with first order surveyor's attitude. 🙂
> A lot of good info already mentioned. 1 thing we do that hasn't been mentioned-
> when measuring up to the prism on the backsight, we turn the prism parallel to the ground and measure to the side of the target. I think this helps to better identify a more precise point to measure to without as much eyeballing/rubbernecking.
> This does give a slant height and you can read/estimate it to 0.005'. Our targets are 0.59' wide, so the our "radius" is 0.295' - - your HS for your target will be
> .
> .
> HS= SQRT [slantheight^2-radius^2]
>
> (for most applications 4-6' the HS will be about 0.005' less than your slant height.)
>
> Don't forget to turn your target back to it's correct position oriented toward the instrument.... otherwise when you try to orient the instrument on the backsight- you'll do a facepalm and "commence the walk of shame" back to the backsight. Remember- It doesn't take any longer to complete an accurate/precise measure-up than it does to do a crappy/sloppy one- you just see the results in your vertical....
>
> 
Aloha, Dan: Thank you for additional thoughts.
I don't have leveling instrument to run it separately at this time. 🙁
However, I am checking on eBay for rotating optical plummet...
> If you're really trying to be that accurate with the elevations I would carry HI on the traverse, but nothing beats a good old fashioned level loop. Run a closed level loop turning on each traverse point.
>
> Also, 3 optical or laser plummet tribrachs are a requirement for this procedure in my opinion. That's the way I've always leap frogged.
Aloha, Jim: That made me feel better!
Yswami
You said:
>
> I don't have leveling instrument to run it separately at this time. 🙁
>
But, you do have a leveling instrument; your total station. Measuring up from your baseline or traverse point will get you close, but there is always some slack with elevations obtained this way.
If you run a trig level run, where you never set OVER your baseline, but shoot them on the side, as described in the paper linked in this thread:
https://surveyorconnect.com/index.php?mode=thread&id=247446#p247492
you will have pretty good elevations. It takes a while to get comfortable with the process, but then, you, as an amateur have done very well learning the basics of measuring and adjustments, so, you can probably grasp this too.
Good luck.
Ken
Aloha, Ken:
First of all thanks for your vote of confidence for this amateur! 🙂
I have read Jesse Kozlowski papers to understand trig. leveling. Obviously, I didn't understand it as well as I thought I did. It sinks in my brain better when I actually practice anything I want to learn few times.
When Dan's post above said run the level separately...my mind was thinking about one those Topcon DL series levels!
One of the most revealing and enlightening statement from your post was this, "If you run a trig level run, where you never set OVER your baseline, but shoot them on the side.." Thank you for that!
Aloha!
> Yswami
>
> You said:
> >
> > I don't have leveling instrument to run it separately at this time. 🙁
> >
> But, you do have a leveling instrument; your total station. Measuring up from your baseline or traverse point will get you close, but there is always some slack with elevations obtained this way.
>
> If you run a trig level run, where you never set OVER your baseline, but shoot them on the side, as described in the paper linked in this thread:
>
>> https://surveyorconnect.com/index.php?mode=thread&id=247446#p247492
>
> you will have pretty good elevations. It takes a while to get comfortable with the process, but then, you, as an amateur have done very well learning the basics of measuring and adjustments, so, you can probably grasp this too.
>
> Good luck.
>
> Ken
> when measuring up to the prism on the backsight, we turn the prism parallel to the ground and measure to the side of the target
I just scratched a horizontal line and Dremeled a notch in the side of the target:
When I take the TS tribrach (no optical plummet) forward while the instrument is on another tribrach I chose my next set up point and set the legs complete with that tribrach and a target, level it with the tribrach bubble then read.
Then I set up the TS in same tribrach and place a mark below it.
You can take heights to the mark and adjust your data recorder settings accordingly.
Before placing mark I read to next station.
That way you can do a backsight /foresight check after incase of concern for bumping legs whilst driving mark.
Obviously drill holes and nails in kerbs pose a challenge if that is the way you want marks placed.
This obviously takes extra care, but on one hand shouldn't be more so than conventional traversing.
Just if things do get knocked you already have an observed point that just needs instrument /target resetting.
Like others said, I don't change tribrachs on a set up point midstream. (target to instrument)
I do like a continuous flow.
That doesn't prove every mark is spot on (exact) in its true position relative to plumbing errors.,but it doesn't introduce an unnecessary potential error.
Personally if I'd thought more I'd have bought targets with no optical plummet in tribrach and same height.
Didn'thhappen, but I'm well satisfied with results.
TS levelling can be a very quick and accurate way to carry verticals. Been a firm believer in that for years.
yswami: I imagine your weather is much better than here. I went to a site yesterday, mainly for recon because I knew what the forecast was, but it was really nasty. Nothing worse than a cold rain. I would much prefer snow than that, which is what it is doing now.
> Aloha, John:
> Thanks for chiming in!
>
> I understand most of it; however, few questions below...
>
> I do remember seeing the images posted in the past with S6 setup on the river bed and you in your canoe next to it!
>
> > I also measure the slope HT to seco mini prisms, and enter that in the DC. But, that is not as accurate as measuring the the instrument.
> This is not clear to me. Could you please clarify how this measurements are done?
Because the mini prisms are not that large, it is difficult to get a straight slope measurement due to the head of the tripod. At times it is easier than others, depending if the tribrach is near the edge of the tripod head. The S6, on the other hand, is larger and easier to measure a direct slope measurement.
>
> > If I want good verticals (trigs), I use the following info: the S6 is 0.196 m above the tribrach plate. The prisms are 0.083 m above the tribrach plate. So, I can easily compute what the prism SHOULD be true vertical, and can change it if needed, usually in the office.
>
> I don't understand this one John... How are you getting these values? We have the height value from ground mark to tripod plate, bottom of the tribrach to its top plate and the bottom of the instrument to it designated mark(s). Where does this values fit in this variables? Sorry if this is a silly question!
Not at all...many total stations and older theodolites all use the same height: 196 mm (T2, DKM2, Zeiss S10, Trimble S6, as well as the Trimble GX scanner, probably others as well). This is the distance above the tribrach plate that the instrument sits in. Similarly, the prism and "hockey puck" adapter that we use are all all 0.083 m. So, if I do not need a ground point, I can easily carry elevations through a traverse with no loss of accuracy due to measuring HI's and HT's. Also, I always know the difference between the HI of the S6 and the HI of the prisms (0.113 m), so that is another check and a correction that can be made in the office.
>
> Thank you so much!
Joe Glidden used to say
that forced centering traverses were great, if you never needed to use that hub ever again. His reasoning was that the tribrach used in the foresight had to be tuned slightly over the point with the instrument. Search the old POB for threads on this.
Food for thought.
Aloha, John: Thank you so much for the detailed explanations!
Forced Centering on POB--Kris Morgan
Aloha, Kris:
I can't believe it you want me to go to the "other" side...err site:-D 😀 😀 Just kidding...I have no problem with POB site;-) Not knowing the history; however, I do sense some sort of rivalry between these two sites:-)
I found a thread on Forced Centering there. Wasn't that many comment from Joe Gildden. There was a link that Mr. Gildden had in one of his post. But the link is no longer working.
It is again obvious--even in that discussion--that there are clearly two views on forced centering. One for adjusting the TS to the center and another one for not touching the tribrach if the TS is not precisely centered on the mark on the ground.
I guess if we call it forced centering then to live by its name the tribrach should not be touched...:-)
Anyways...if you have any more information that was shared by Mr. Gildden, it will be very much appreciated if you could post or email.
Thank you so much Kris as always!
Forced Centering on POB--Kris Morgan
> Anyways...if you have any more information that was shared by Mr. Gildden, it will be very much appreciated if you could post or email....
Aloha my friend,
Mr. Glidden was affectionately known as Jobo....He passed away on Christmas Day, 2013.
I knew Jobo; and cherish every minute, of the few times I got to spend with him. He was a wealth of survey knowledge and shared all of it freely with us on both boards. He knew a lot about railroad surveys and calculations; his presents here is sorely missed....
Here is my opinion on forced centering:
This is a method used to buffer the error in the tribrach: The accuracy you are trying to achieve; with the alignment of the tribrach (and what ever you put in it) and a point on the ground; and the measurement between them. There is one more element in this equation; the tripod. The tripod is the weakest link in the whole set up. It is subject to atmospheric conditions, the sun will heat up 1 side while the other is shaded; it is subject to the ground it is set up on, a tripod will sink into hot asphalt, especially with a heavy robot sitting on top of it; it is subject to the banging around it takes by clamping your data collector to it and changing out the gun and glass.
If I traverse with this method, I always adjust the tribrach a little if it needs it; because I don't trust the tripod to stay in 1 spot very long and if it is more than a little; I will run that point again, just to make sure.
Aloha my friend; i hope you enjoy a great day, I know I will.
Dougie
Forced Centering on POB--Kris Morgan
Aloha, Dougie:
Thank you for sharing a bit more information about Mr. Glidden. He may not be with us physically but he for sure lives in the heart of those he touched and those who come to know him later like me. If a man can live his life in such a way that others constantly remember him, make references about him for who he was and his great contribution then he truly fulfilled the purpose of his incarnation!
Dougie, thank you for pointing out another variable that contributes another error. It is very much appreciated.
I love your signature...always affirming you will have a great day. I am having a great day too!
With aloha from Kauai!
> > Anyways...if you have any more information that was shared by Mr. Gildden, it will be very much appreciated if you could post or email....
>
>
>
> Aloha my friend,
>
> Mr. Glidden was affectionately known as Jobo....He passed away on Christmas Day, 2013.
>
> I knew Jobo; and cherish every minute, of the few times I got to spend with him. He was a wealth of survey knowledge and shared all of it freely with us on both boards. He knew a lot about railroad surveys and calculations; his presents here is sorely missed....
>
> Here is my opinion on forced centering:
>
> This is a method used to buffer the error in the tribrach: The accuracy you are trying to achieve; with the alignment of the tribrach (and what ever you put in it) and a point on the ground; and the measurement between them. There is one more element in this equation; the tripod. The tripod is the weakest link in the whole set up. It is subject to atmospheric conditions, the sun will heat up 1 side while the other is shaded; it is subject to the ground it is set up on, a tripod will sink into hot asphalt, especially with a heavy robot sitting on top of it; it is subject to the banging around it takes by clamping your data collector to it and changing out the gun and glass.
>
> If I traverse with this method, I always adjust the tribrach a little if it needs it; because I don't trust the tripod to stay in 1 spot very long and if it is more than a little; I will run that point again, just to make sure.
>
> Aloha my friend; i hope you enjoy a great day, I know I will.
>
> Dougie